Color display tube with elongated phosphor dots and shadow mask apertures

ABSTRACT

A shadow mask tube having elongated apertures arranged in rows with the ends of apertures in each row extending between apertures in the next row to improve light emission and eliminate moire patterns caused by scanning non-emissive areas.

I United States Patent 1191 1111 3,828,216

Fuse 1 Aug. 6, 1974 COLOR DISPLAY TUBE WITH 3,448,316 6/1969 Yoshida eta1. 313/70 ELONGATED PHOSPHOR DOTS AND 3,663,854 /1972 Tsuneta et a1313/92 B X SHADOW MASK APER Es FOREIGN PATENTS OR APPLICATIONS [75]Inventor: Yum Fuse Japan 393 417 10/1965 Switzerland 313/85 s [73]Assignee: Sony Corporation, Tokyo, Japan 807Zl29 1/1959 Great Britain.led Ja 16 1973 1,023,334 3/1966 Great Britain 313/85 S [2]] App! 324,133Primary ExaminerRobert Segal Related Application Data Attorney, Agent,or Firm--Lewis H. Eslinger, Esq.; [63] Continuation of Ser. No. 114,981,Feb. 12, 1971, Alvin Sinderbrand, Esq.

abandoned.

[] Foreign Application Priority Data Feb. 14, 1970 Japan -12886 [57]ABSTRACT A shadow mask tube having elongated apertures arg% 5 ranged inrows with the ends of apertures in each row d 313/85 92 B extendingbetween apertures in the next row to im- 1 0 prove light emission andeliminate moire patterns References Cited caused by scanningnon-emissive areas.

UNITED STATES PATENTS 6 Claims 5 Drawing Figures 2,922,073 1/1960Oestreicher 313/ S 2 7 a9 7-Lv L i g L X 3: Mr .L

PAIENIEB 5W4 SHEEI 1 0f 2 INVENTOR.

Yuzo E15 BY ATTORNEY 2 COLOR DISPLAY TUBE WITH ELONGATED PHOSPI'IOR DOTSAND SHADOW MASK APERTURES This is a continuation of application Ser. No.114,981, filed Feb. 12, 1971, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the field of shadow mask cathode ray tubes for color displayand particularly to an improved shadow mask arrangement for such tubes.

2. Description of the Prior Art Apertured shadow mask cathode ray tubesfor color television have been made in the past so that each aperturewas circular and was equally spaced from six surrounding apertures. Eachaperture controlled the access path to three circular phosphor elementssubstantially equidistant from that aperture. While it was thought thatall of the elements should be of the same diameter and contiguous withsix other elements, experience has shown that the phosphor elementsshould be smaller in diameter and should have some space around them.Preferably this surrounding area is made black to improve the contrastratio of the color television picture. The apertures are also madesmaller than they theoretically could be, which makes the mask moreopaque to electron beams than it might be and reduces the maximumpossible brightness of the picture. Another adverse effect is that thescanning electron beam (or beams) may follow a path that strikes mostlyopaque sections of the shadow mask rather than sections havingapertures. For example, one scanning line may pass through the centersof a row of apertures and may therefore cause the maximum amount oflight to be emitted. The next line may strike only metal portions of themask and may pass between two rows of apertures. This latter beam wouldcause little or no light to be emitted from the phosphor screen.Depending on the relative spacing of the scanning lines and theapertures, and depending also upon the amount and location of thosesections of the screen not coated with light-emitting phosphor, a moirepattern of alternate light and dark strips may be produced in thetelevision picture.

It is one of the primary objects of the present invention to provide ashadow mask arrangement that minimizes or eliminates moire patterns inthe television picture and increases the amount of screen area capableof emitting light.

It is another object of the invention to provide a shadow mask havingapertures of more nearly optimum arrangement and spacing than inprevious shadow mask tubes.

Other object will become apparent from the following specification anddrawings.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the invention, ashadow mask with non-circular apertures is provided. The apertures arepreferrably arranged so that their longer dimensions are perpendicularto the scanning lines of the color television picture. Furthermore, thespacing between the most closely adjacent apertures in the directionperpendicular to the scanning lines is approximately equal to thespacing between the most closely adjacent apertures in the direction ofthe scanning lines, thereby equalizing the resolution of the colortelevision picture in the horizontal and vertical directions. Also inaccordance with the invention, the elongated apertures in one horizontalrow are displaced from the next adjacent horizontal row by a distanceless than the vertical dimension of the apertures, thus producing someinterleaving of elongated apertures in adjacent rows. Ideally, theapertures may have a rhombic shape, but they can also be more or less inthe shape of elongated hexagons or even ellipses. The operation of thetube may be further improved by making the apertures larger in size thanthe phosphor elements behind them.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows an arrangement of round phosphor elements on a colortelevision cathode ray tube constructed in accordance with the priorart;

FIG. 2 is an array of square phosphor elements arranged for use with amodified shadow mask;

FIG. 3 is an array of rectangular phosphor elements arranged in a moreefficient pattern than the phosphor elements of FIGS. 1 and 2;

FIG. 4 shows an array of rhombic phosphor elements and shadow maskapertures according to the present invention; and

FIG. 5 is a cross-sectional view of a color television tube constructedto incorporate the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Basically, FIG. 1 shows a screen 10with an array of circular phosphor elements of maximum permissible sizeso that each element is contiguous with six others surrounding it. Theelements are arranged in horizontal rows in a repetitive pattern and areidentified as R, B, and G to correspond to the fact that all elementsbearing the letter R emit red light, all those bearing the letter B emitblue light, and all those bearing the letter G emit green light. Thespace 11 between the round phosphor elements is supposed to be incapableof emitting light and therefore has been shown shaded.

FIG. 1 also shows the perpendicular projection of holes in the aperturemask that controls the access of electrons to the individual phosphorelements. For example, the hole 12 is centered between three phosphorelements 13-15, which emit, respectively, green, red, and blue light.Also shown is a perpendicular projection of the paths of the electronsthat pass through the aperture 12 on the way to the three phosphorelements 13-15. The size of the aperture 12 is such that only thecentral area of the phosphor elements 13-15 is struck by electrons andthe annular region surrounding this central area is shielded from all ofthe electron beams. As a result, this surrounding area may be a materialother than the phosphor and in particular it may be carbon or manganesedioxide so that it absorbs light, thereby improving the contrast ratioof the color television picture.

The arrangement of phosphor elements 13-15 in triangular groups producesthe closest spacing of the three primary color elemental light sourcesand would appear to produce the highest resolution of a color televisionpicture. However, due to the fact that the apertures l2 and the phosphorelements 13-15 are arranged in triangular arrays of densely packedequilateral triangles, the pitch spacing P between apertureshorizontally displaced on the same line is different from the pitchspacing P between apertures spaced vertically in the same column. As amatter of fact, the pitch spacing P is 3 times the pitch spacing PAnother defeet in the color screen in FIG. 1 is the relatively largearea of the screen that produces no light due to the limited size of theapertures 12 and the excited phosphor areas. As shown in the drawing,there are horizontal bands having a width W from which no light can beemitted. If these bands are spaced apart by a distance that differs fromthe distance between scanning lines of the color television picture, oris in a different direction, a moire pattern will be produced which willadversely affect the quality of the television picture.

FIG. 2 shows a screen 16 in which an attempt has been made to achievegreater light output by arranging the phosphor elements 17-19 as squaresinstead of circles. This eliminates the area that is not coated with anyphosphor, but the screen 16 in FIG. 2 still has apertures 21 smaller insize than the size of the phosphor elements. Therefore, there arehorizontal lines of width W from which no light will be emitted andthese can produce the same type of undesirable moire effect as thecorresponding bands of width W in the screen 10 of FIG. 1.

FIG. 3 shows a modified screen 22 having rectangular phosphor elements23-25. The ratioof width to height of these rectangular phosphorelements is such that the spacing between the most closely adjacentphosphor elements of the same color, for example, the phosphor elements23 that emit green light, is reduced to a minimum. Lines through thecenter ofthe most closely adjacent phosphor elements make angles ofapproximately 45 with respect to the horizontal and vertical. Inaddition, the vertical pitch spacing P is approximately equal to thehorizontal pitch spacing P which results in uniform resolution in thehorizontal and vertical directions. However, there is still thepossibility of producing a moire pattern due'to'bandsof width W fromwhich no light is emitted.

FIG. 4 shows a fluorescent screen 27 with an array of phosphor elementsaccording to the present invention. Each phosphor element is in theshape of a rhombus, and, as before, the elements are divided into groupscapable of emitting light in the three primary colors. The elements 28emit green light, the elements 29 emit blue light, and the elements 30emit red light.

The rhombic phosphor elements have their major dimension in the verticaldirection and their minor dimension in the horizontal direction. As aresult, the

phosphor elements may be considered to be arrangedin horizontal rows Land elements of the same color characteristic are arranged in verticalcolumns Ly.

The apertures and the shadow mask to be used with the screen 27 areindicated by reference numeral 31 and are also rhombic. Unlike theapertures in the embodiments shown in FIGS. 1-3, the apertures 31 of onerow overlap the apertures 31 in the adjoining row. The width of eachrow, for example as indicated by X, and X is determined by the maximumdimension of the apertures and the spacing between a line through thecenters of the apertures in each of two adjoining rows is less than thewidth of those rows. As shown, the apertures 31 in each row are partlyinterleaved with the apertures 31in the next adjoining row so that everyhorizontal line or nearly horizontal line can be traced out by theelectron beam that passes through apertures in either one row or thenext adjoining row. Consequently, there is no significant moire patternproduced by this screen of FIG. 4 even if the apertures 31 are somewhatsmaller than the phosphor elements 28-30.

The rhombic shape of the apertures 31 and of the phosphor elements foreach of the individual colors, for example the elements 28, is such thatthe vertical spacing P is approximately equal to the horizontal spacingP thereby equalizing the resolution between the horizontal and verticaldirections. In addition, the spacing of the nearest adjacent apertures31 is such that these apertures lie along lines that make 45 angles withrespect to the horizontal and vertical direction.

In order to make the aperture mask 27 sufficiently rigid, the verticallyadjoining apertures must not run into each other. As may be seen, makingthe apertures 31 even slightly smaller than the phosphor elementspermits the closest bands of vertically adjacent apertures to be spacedby a substantial distance d. As a result, the mask 27 is strong enoughto stand up under commercial usage.

Although the preferred shape of the apertures 31 is rhombic, they may beslightly flattened off at the top and bottom or on the sides to formelongated hexagons, or they may be rounded off to form ellipses.

FIG. 5 shows a complete cathode ray tube 32 constructed according to theinvention. This tube is basically of the same type shown in U.S. Pat.No. 3,448,316 and comprises three cathodes 33-35 that emit,respectively, beams of electrons to energize phosphor elements thatproduce green, blue, and red light. The cathodes 33-35 are supported inproperly spaced relationship to a common first grid, or controlelectrode, 36 which has three apertures 37-39 aligned with the cathodes33-35, respectively. The tube has a second grid electrode 41 withapertures 42-44 aligned with the apertures 37-39. Beyond the electrode41 is an anode 46 which, together with the electrode 41, produces acommon lens field 47 that causes all of the electron beams from thecathodes 33-35 to converge to the center of an electron lens 48 so as tominimize deleterious effects due primarily to spherical aberration andcoma. The central rays of the three electron beams are indicated byreference numerals 49-51 and they are modulated with informationcorresponding, respectively, to green, red, and blue portions of atelevision picture.

The main electron lens 48 is formed by electrostatic fields of the anode46, a focusing electrode 52, and another anode section 53 directlyelectrically connected to the anode 46. The lens thus formed may also bereferred to as an einzel lens. Beyond the lens field is a set ofconverging deflection'electrodes 54-57 of which the electrodes 55 and 56are at one potential, preferably the potential of the anodes 46 and 53and the electrodes 54 and 57 are at a negative potential with respect tothe electrodes 55 and 56. As a result, the electron beam 49 is notsubjected to any deflecting forces and continues directly along theaxis, and the electron beams 50 and 51 are deflected back toward theaxis. The inner wall of the tube 32 has a conductive coating 58 that iselectrically connected to the anodes 46 and 53.

The electron beams converge at a shadow mask 59 in which the apertures31 of FIG. 4 are located. The shadow mask is a thin sheet of metalsupported by a rim 61 held in place by springs 62 on ceramic studs 63that determine the exact location of the mask. The mask is curved inaccordance with the curvature of the face plate 64 of the tuve 32, andthe inner surface of this face plate is the screen 27 on which thephosphor elements 28-30 of FIG. 4 are deposited. The orientation of theapertures 31 in the mask 59 is such that the long dimension of theseapertures is perpendicular to the plane of the drawing and the shortdimension is in the plane of the drawing. A deflection yoke 66 islocated on the neck of the tube to deflect the electron beams 49-51across the surface of the mask 59, and the mask is so oriented that theline deflection of the beams in forming a television picture isperpendicular to the long dimension of the apertures 31 and parallel tothe short dimension of these apertures.

The arrangement of the beam-forming electrodes in the tube in FIG. 5 issuch that all three of the beams 49-51 are in the same plane, whichshould be oriented so that it is perpendicular to the major dimension ofthe apertures 31. As the beams pass through the apertures, they do soalong paths that lead to specific sets of the phosphor elements on thescreen. The beam 49, for example, passes through the apertures 31 alongpaths that lead only to phosphor elements that emit green light, whichare the phosphor elements 38 in FIG. 4. The beam 50 passes through theapertures 31 along paths that lead only to the elements 30 that emit redlight, and the beam 51 passes through-the apertures 31 along paths thatlead only to the elements 29 that emit blue light.

As an alternative to arranging the beam-forming electrodes so that thebeams 49-51 are in line with each other, they may be arranged in whathas come to be known as a delta configuration corresponding to thetriangular array of phosphor elements. If the beams are so arranged inthe present case for use with a screen of the type of screen 27 in FIG.4, two of the beams should strike the screen along a line parallel tothe direction of the scanning lines and parallel to the smallerdimension of the apertures 31 and the third beam should lie along aperpendicular bisector of the line joining the other two beams. Thisperpendicular bisector is parallel to the major dimension of theapertures 31. As a further alternative a three-gun structure could beused instead of the single-gun structure shown to direct beams towardthe shadow mask 59.

What is claimed is:

l. A cathode ray tube comprising:

A. Means for generating a plurality of electron beams and for convergingsaid beams from originating points spaced apart in a flat plane;

B. A viewing screen;

C. An array of phosphor elements arranged in a repetitive pattern ofgroups thereof at predetermined locations on said screen, with each ofsaid groups including phosphor elements each relating to a respectiveone of said electron beams and emitting light of a characteristic colorwhen impinged upon by the respective beam; and

D. A shadow mask positioned adjacent said screen and having an array ofapertures each located in correspondence to a respective one of saidgroups of phosphor elements, said apertures and said phosphor elementsbeing longer in one direction than in a direction substantiallyperpendicular to said one direction and arranged in rows in saidperpendicular direction which is generally parallel to said flat plane,the width of each of said rows being defined by the lengths of saidapertures in that row, the centers of adjoining rows being spaced apartby a distance less than the width of each of said adjoining rows, saidapertures of each of said rows being interleaved with said apertures ofeach of the adjoining rows, each of said apertures in each of said rowsbeing substantially aligned in the direction of the aperture length withone of said apertures two rows therefrom, and the center-to-centerspacing between the aligned apertures two rows apart being substantiallyequal to the center-tocenter spacing between adjacent ones of saidapertures in the same row.

2. The cathode ray tube of claim 1 in which said apertures are rhombic.

3. The cathode ray tube of claim 1 in which lines joining the centers ofthe nearest adjacent apertures not in the same row make an angle ofapproximately 45 with respect to said rows.

4. A cathode ray tube according to claim 1; in which said phosphorelements are of rhombic shape and substantially cover the entire area ofsaid screen.

5. A cathode ray tube according to claim 1; in which said apertures andphosphor elements have substantially similar shapes.

6. A cathode ray tube according to claim 5; in which said similar shapesof the apertures and phosphor elements are substantially rhombic.

* III

1. A cathode ray tube comprising: A. Means for generating a plurality ofelectron beams and for converging said beams from originating pointsspaced apart in a flat plane; B. A viewing screen; C. An array ofphosphor elements arranged in a repetitive pattern of groups thereof atpredetermined locations on said screen, with each of said groupsincluding phosphor elements each relating to a respective one of saidelectron beams and emitting light of a characteristic color whenimpinged upon by the respective beam; and D. A shadow mask positionedadjacent said screen and having an array of apertures each located incorrespondence to a respective one of said groups of phosphor elements,said apertures and said phosphor elements being longer in one directionthan in a direction substantially perpendicular to said one directionand arranged in rows in said perpendicular direction which is generallyparallel to said flat plane, the width of each of said rows beingdefined by the lengths of said apertures in that row, the centers ofadjoining rows being spaced apart by a distance less than the width ofeach of said adjoining rows, said apertures of each of said rows beinginterleaved with said apertures of each of the adjoining rows, each ofsaid apertures in each of said rows being substantially aligned in thedirection of the aperture length with one of said apertures two rowstherefrom, and the center-to-center spacing between the alignedapertures two rows apart being substantially equal to thecenter-to-center spacing between adjacent ones of said apertures in thesame row.
 2. The cathode ray tube of claim 1 in which said apertures arerhombic.
 3. The cathode ray tube of claim 1 in which lines joining thecenters of the nearest adjacent apertures not in the same row make anangle of approximately 45* with respect to said rows.
 4. A cathode raytube according to claim 1; in which said phosphor elements are ofrhombic shape and substantially cover the entire area of said screen. 5.A cathode ray tube according to claim 1; in which said apertures andphosphor elements have substantially similar shapes.
 6. A cathode raytube according to claim 5; in which said similar shapes of the aperturesand phosphor elements are substantially rhombic.